Ingredients
4 crisp baking apples, such as Jonagold or Golden Delicious
3 medium-sized sweet potatoes, about 2 pounds
6 shallots
4 tablespoons olive oil, divided
1 teaspoon kosher salt, divided
1/2 teaspoon freshly ground pepper
8 ounces soft goat cheese
4 tablespoons creamery butter, room temperature, plus more for pan
3 tablespoons whole-grain mustard, divided
8 5-6 ounce buffalo tenderloin steaks
1 cup apple cider
2 tablespoons apple cider vinegar
Preparation
Preheat the oven to 425.
Peel, quarter and core the apples, then slice into eighths. Toss the apples in a large bowl with one tablespoon olive oil and 1/4 teaspoon of kosher salt. Arrange in a single layer on a baking sheet.
Peel sweet potatoes and slice lengthwise into 1/4" thick planks. Toss with another tablespoon olive oil and another 1/4 teaspoon kosher salt. Arrange in a single layer on a second baking sheet.
Peel and half the shallots. Add to the baking sheet with the sweet potatoes.
Roast all vegetables in the preheated oven until tender and brown in spots, 25-30 minutes, turning once. Reduce the oven to 375.
To assemble the gratin, butter a 12-inch oval baker. Layer 1/3 of the sweet potatoes, 1/2 of the apples, and 1/2 of the shallots in the baker, then season with pepper, and dot with 1/3 of the butter, 1/3 of the goat cheese, and about a tablespoon of mustard. Add another layer of sweet potatoes, then the remaining apples, shallots, more pepper, another tablespoon of mustard, and a second 1/3 of the butter and goat cheese. Top the gratin with the remaining sweet potatoes and compress the dish slightly. Finish with the remaining butter and goat cheese. Bake the gratin for 20-30 minutes, until richly browned on top.
While the gratin bakes, pat dry the buffalo tenderloins, then oil all sides of each with the remaining two tablespoons of olive oil. Season with the remaining 1/2 teaspoon of salt. Preheat a large saute pan or cast iron skillet over high heat. When the pan is smoking, sear the tenderloin steaks, about 2 minutes per side, working in 2 batches. Remove the steaks to a serving platter, tent with foil, and rest at least 5 minutes.
When all of the steaks are cooked, deglaze the pan with the apple cider. Add vinegar and final tablespoon of mustard, and simmer pan sauce until reduced to a glaze. Spoon over tenderloin steaks and serve immediately, accompanied by the gratin.
